The present disclosure relates to burner assemblies, and particularly to oxygen-fuel burner assemblies. More particularly, the present disclosure relates to pulverized solid fuel combustion systems. Many types of coal and other solid fuels can be burned successfully in pulverized form. Coal is pulverized and delivered to fuel-burning equipment and then combusted in a furnace to produce heat for various industrial purposes. A burner is used to “fire” pulverized coal and other solid fuels.
Oxy-fuel combustion is a facilitating technology in the overall plan to reduce greenhouse gases produced from the burning of fossil fuels. Utilizing pure or nearly pure (>90% v/v) oxygen instead of atmospheric air for combustion, removes atmospheric nitrogen (78% v/v) from the fuel burning process and significantly reduces the exhausted combustion products volume by over 75% for an equivalent fuel input. The elimination of atmospheric nitrogen from the exhaust gases concentrates the produced H2O and CO2 in the exhaust stream. This facilitates CO2 capture through various means such as compression. (Exhaust products of combustion are also known as flue gases, or furnace gases throughout industry).
Coal fired power plants also utilize large volumes of blower driven atmospheric air for transport of the pulverized coal particles to the burner. The term for this transport air in the industry is “primary air”. In the overall effort to eliminate atmospheric nitrogen from the process, it is also desired to eliminate the use of this atmospheric air for transport of the pulverized fuel. By substituting conditioned recycled flue gas for the primary air, the pulverized fuel would be transported by a blower driven stream of gases composed mostly (>75% v/v) of CO2. The recycled flue gas would be mostly inert, therefore, having the fuel transported and mixed with an inert gas, increases the possibility of flame instability, poor combustion performance and unacceptable pollutant emissions.
The flue gas from oxy-fuel combustion, conditioned and cleaned in preparation for recycle use, would contain over 75% carbon dioxide (CO2). CO2 is an inert gas and is commonly used in fire extinguishers. Its presence in the burner mixing and flame zones could create flame instability, poor combustion performance, unacceptable percentages of unburned fuel or complete extinction of the flame. In addition, the transport CO2 would lower peak flame temperatures which would reduce the radiant energy transmitted from the flame to the radiant section of the boiler.
A burner designed to operate with recycled flue gas while maintaining flame stability, increased peak flame temperature and producing industry accepted performance, is required to advance carbon capture technology for fossil fuel fired applications.
According to the present disclosure, a burner assembly is provided for combining oxygen and fluidized, pulverized, solid fuel to produce a flame. The burner assembly includes a primary oxygen supply tube adapted to receive a stream of oxygen and a solid fuel conduit arranged to extend through the primary oxygen supply tube to convey a stream of fluidized, pulverized, solid fuel into a flame chamber.
Oxygen flowing through the primary oxygen supply tube passes through a first set of oxygen-injection ports formed or otherwise installed within in the solid fuel conduit and then mixes with fluidized, pulverized, solid fuel passing through the solid fuel conduit. The first set of oxygen-injection ports is arranged so that oxygen flowing there through enters the solid fuel conduit substantially tangential thereto.
Oxygen flowing through the primary oxygen supply tube may also pass through a second set of oxygen-injection ports formed or otherwise installed in the solid fuel conduit and then mix with the fluidized, pulverized, solid fuel passing through the solid fuel conduit. The second set of oxygen-injection ports is arranged so that oxygen flowing there through enters the solid fuel conduit predominantly tangential thereto but with a radial component.
Thus, an oxygen-fuel mixture is created in a downstream portion of the solid fuel conduit and discharged into the flame chamber. This mixture is ignited in the flame chamber to produce a flame.
In illustrative embodiments of the disclosure, the solid fuel conduit extends into and through the primary oxygen supply tube to define an annular primary oxygen flow passage extending around and along an annular exterior surface of the solid fuel conduit in a direction toward the flame chamber. Oxygen flows through this annular primary oxygen flow passage to reach inlets of the oxygen-injection ports in the annular exterior surface of the solid fuel conduit.
In one embodiment, the solid fuel conduit includes a solid-fuel conduit and an oxygen-fuel nozzle coupled to or integral with the solid-fuel conduit and formed to include the oxygen-injection holes. Oxygen and fluidized, pulverized, solid fuel are mixed in the nozzle to create a combustible mixture that is then discharged into the flame chamber and ignited to produce a flame.
In illustrative embodiments of the disclosure, means is provided for mixing some of the oxygen extant in the primary oxygen flow passage provided in the primary oxygen conduit with the oxygen-fuel mixture that is discharged from the solid fuel conduit into the flame chamber. In this case, a first portion of the oxygen flowing through the primary oxygen flow passage is mixed with the stream of fluidized, pulverized, solid fuel just before that fuel exits the solid fuel conduit. A remaining portion of the oxygen flowing through the primary oxygen flow passage is mixed with the oxygenated stream of fluidized, pulverized, solid fuel in a region located outside the solid fuel conduit and near an oxygen-fuel outlet opening formed therein to provide supplemental oxygen to that oxygenated fuel stream and to sweep the end of the oxygen-fuel outlet of ash and the like that may form or be deposited there.
In other illustrative embodiments, a secondary oxygen conduit is provided about the primary oxygen supply tube, forming a secondary oxygen passage therebetween. In such embodiments, oxygen flowing through the secondary oxygen passage is mixed with the oxygenated steam of fluidized, pulverized, solid fuel in a region located outside the solid fuel conduit and near the oxygen-fuel outlet opening formed in the solid fuel conduit to provide supplemental oxygen to that oxygenated fuel stream.
Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived.